Net Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Comprehensive Income [Line Items]
Balance at January 1, 2013			$ 20,258	$ 20,006
Other comprehensive income before reclassification, net of tax			(14,365)	811
Reclassifications from accumulated other comprehensive income, net of tax			71	98
Current period change in other comprehensive income, net of tax	(12,496)	1,529	(14,294)	909
Balance at June 30, 2013	5,964	20,915	5,964	20,915
Balance at January 1, 2013			(8,946)	(6,758)
Other comprehensive income before reclassification, net of tax			0	0
Reclassifications from accumulated other comprehensive income, net of tax			557	420
Current period change in other comprehensive income, net of tax	339	210	557	420
Balance at June 30, 2013	(8,389)	(6,338)	(8,389)	(6,338)
Balance at January 1, 2013			11,312	13,248
Other comprehensive income before reclassification, net of tax			(14,365)	811
Reclassifications from accumulated other comprehensive income, net of tax			628	518
Current period change in other comprehensive income, net of tax			(13,737)	1,329
Balance at June 30, 2013	$ (2,425)	$ 14,577	$ (2,425)	$ 14,577